Electrostatic data display



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PERCY J. BARNES AGE NT Aug. 31, 1965 P. J. BARNES ELECTROSTATIC DATA DISPLAY Filed Dec. 24, 1959 4 Sheets-Sheet 2 VENTOR.

I 6 PERCY J. BARNES WWW KW AGENT Aug. 31, 1965 P. J. BARNES 3, 7

ELECTROSTATIC DATA DISPLAY Filed Dec. 24, 1959 4 Sheets-Sheet :5

INVENTOR.

PERCY J. BARNES r BY AGENT Au 31, 1965 P. J. BARNES 3,204,247

ELECTROSTATIC DATA DISPLAY Filed Dec. 24, 1959 4 Sheets-Sheet 4 BY W W AGENT Q INVENTOR. a H PERCY J. BARNES United States Patent 3,204,247 ELECTRUSTATIC DATA DlSlPLAY Percy J. Barnes, Wilmington, Deh, assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Filed Dec. 24, 1959, Ser. No. 861,906 14 Claims. (Cl. 346-74) This invention relates to electrostatic reproduction and apparatus therefor.

The art of electrostatic printing consists basically of the production on a charge-retentive surface of a pattern of electrical charges whose distribution is later indicated by the adherence to the charged areas of a visible substance analogously denoted as ink, although it is commonly a particulate or powdered non-liquid. The application of the ink to the charge-retentive medium in such fashion that it adheres visibly differently to the charged areas than to the non-charged or oppositely charged areas is known, by obvious analogy, as development; and any process aimed at making the adherence of the ink permanent even after dissipation of the charges which originally caused its adherence is known, by similar analogy, as fixing.

Some references pertaining to the art of electrostatic printing are the following applications for patents; they have all been assigned to the assignee of the present invention: United States patent application Serial No. 443,646, filed July 15, 1954 by Epstein and lnnes, now US. Patent No. 3,012,839; United States patent application Serial No. 714,767, filed February 12, 1958 by Epstein and Benn and now forfeited in favor of continuing application Serial No. 255,715. A publication is The Electrographic Recording Technique by H. Epstein, Proceedings of the Western Joint Computer Conference, March 1955.

Most of the efforts of the practitioners and investigators of the art of electrostatic printing have been aimed at the creation of charge patterns and the permanent attachment of ink. However, some transfer processes are known in which ink is formed into a pattern on a dielectric surface by the electrostatic process is then transferred by some mechanical means to another base, and the residual charge on the dielectric must be removed to prepare the dielectric for resuse by the formation of a different pattern of charges upon its surface. The removal of charge is often performed by ioninzing the air adjacent to the dielectric surface, either by corona discharge or by radioactive emanations; or the dielectric may be brought into an extremely humid atmosphere, or even immersed in a conductive liquid. The excellent insulating qualities of many modern dielectrics such as Mylar render such special measures for the destruction of charge patterns necessary. It has, for example, been found that in the absence of such special measure a tape of such material preserved in an office at ordinary humidities is capable of retaining a charge pattern for a quarter of a year and, upon develop ment after that period, presenting a perfectly legible image. It is evident that material capable of retaining electric charges for such a long period must be an insulator of extremely high resistivity or low conductivity and it is well known that all such insulators manifest a dielectric constant greater than unity, that of free space. Thus, although the term dielectrics is commonly used in the art to describe such materials, they may equally well be described as high resistivity or charge retentive or electric charge retentive media or materials.

It is described in application for United States Patent, Serial No. 714,767, filed February 12, 1958 by Herman Epstein and Robert E. Benn, Electrographic Recording Process, and now forfeited in favor of continuing application Serial No. 255,715, which applications are assigned to the assignee of this application, how a pattern of charges 3,204,247 Patented Aug. 31, 1965 ice deposited upon a dielectric medium having a conductive backing may be rendered visible, or developed, by being drawn through a mass of electrically conductive particulate ink which mass is in electrical connection with the conductive backing of the medium. It is an observed fact, essential to the operativeness of the invention of the referenced patent application, that the electrically conductive particulate ink mass does not, as might have been expected a priori, merely discharge the dielectric medium and leave it to pass from the mass of ink devoid both of charges and visible pattern; instead, ink particles cling to the dielectric surface wherever charges have been deposited on the dielectric, thus rendering the charge pattern visible. This effect is not a critical one, producible only sporadically and with painstaking control of critical conditions, but instead a highly reliable and reproducible effect which has been preferred for use in reproducing equipment where reliability is essential.

In many circumstances, a need exists for convenient means to display data or information by symbols, with the further requirement that such information be readily changed and replaced with other, more pertitnent or more recent. A human operator transcribing upon a blackboard with chalk can achieve this, but with limitations of speed and accuracy, and with the further limitations that the location of the display must be reasonably accessible to the human operator. The application of conventional electrostatic printing to the provision of data symbols for display achieves speed and accuracy; but conventional application involves the consumption of record medium and ink. My invention provides a data display in which the record medium, after use, is freed of both adherent ink and impressed electric charges and made available for repeated use. If desired, the ink also may be returned to the store. Thus the extreme reliability and high speed of electrostatic recording are rendered additionally advantageous in being combined with operativeness with relatively infrequent human access to the display for maintenance or replacement of supplies. in my specification and description hereinafter, I teach the achievement of such ends by the use of discharge methods previously known in the art.

An invention of Richard S. Howell, the subject of an application for United States patent entitled Erasure of Developed Images, filed December 24, 1959, Serial No. 861,927 and assigned to the assignee of this application, now US. Patent No. 3,108,895, issued October 29, 1963, is a method of divesting a dielectric medium which bears a charge pattern rendered visible by development with particulate ink, as described in the preceding paragraph of this specification, by passing the developed dielectric medium a second time through a mass of conductive ink identical with that employed in the original developing process, but with some means provided for rendering it difficult for the ink in contact with the surface of the dielectric medium to move along through the mass of ink with the moving dielectric medium. His invention includes an application of this method to a form of data display device in which a common container or store is used for the ink required for both the developer and the erasing station of his invention.

Thus it'is an object of my invention to provide a display device embodying erasing means which render the recording medium and, preferably, the developing medium, available for repeated use without replenishment of any kind.

It is another object of my invention to provide a display device which may be operated for long periods of time for the display of different symbols of messages with only infrequent replenishment of supplies.

FIGURE 1 is a schematic view representing a recording e1) station for applying electric charge patterns to a dielectric tape surface, a developing station for rendering such pat terns visible by adherence of particulate ink, a viewing station for viewing the patterns thus made visi le, and an erasing station for removing both the ink and the charge pattern from the tape to render it available for reuse;

FIGURE 2 is a schematic View representing a recording station for applying electric charge patterns to a dielectric tape surface, a developing station for rendering such patterns visible by adherence of particulate ink, a viewing station for viewing the patterns thus made visible, and an erasing station located in the same ink chamber with the developing station;

FIGURE 3 represents a dielectric medium bearing a charge pattern not yet developed, and therefore represented by dotted lines;

FIGURE 4 represents a dielectric medium as in FIG- URE 3, but as it would appear after development with particles of ink pigment adhering in the region of the charge pattern;

FIGURE 5 represents a dielectric medium as in FIG- URES 3 and 4, but after passage through an erasing station which leaves it divested of both charge pattern and ink particles;

FIGURE 6 represents a front view, and FIGURE 7 represents a profile View, of a third embodiment of a device for practicing my invention; and

FIGURES 8 and 9 represent embodiments of my invention alternative to those of the preceding figures.

FIGURES 10A and 10B represent two alternative forms of printing head 12, designated respectively as 12a and 1222.

In FIGURE 1, a dielectric record medium 10 in the form of a tape which may be of Mylar and may have an electrically conductive backing is represented as passing over drive drum 14, which is rotated clockwise by means not shown, and causes tape medium It to pass to the right of the figure between grounded electrode 13 and electrostatic recording head 12, which in consequence of the application to its electrodes of voltages from the apparatus represented by 11, deposits a pattern of invisible electric charges on the upper surface of the dielectric of record medium Ill. The charged medium passes to developing station 24, where a chamber re is represented as containing a mass of powdered particulate electrically conductive ink 18 which becomes attached, by electrostatic attraction, to the dielectric surface of medium Itl in those areas Where electric charges have been stored. Baffles 19, supported by means not represented, serve to prevent any accidental adhesion of ink agglomerate from moving upward with the medium Iii; and vibrator 2%, represented as a rotating polygonal shaft, driven by means not represented, vibrates the medium It) sufiiciently to shake loose any ink accidentally adhering to regions where no charge has been deposited. The preceding brief summary of the operations of electrostatic printing and developing is descriptive of art previously disclosed, in much more detail, in the applications for United States patent by Epstein and Innes and Epstein and Benn, to which referonce has been made in the introductory portion of this specification.

FIGURE 10A represents one form of printing head He having a single row of electrode pins 79 and a common extended electrode 71. FIGURE 103 represents an alternative form of printing head 12b having a number of rows of electrode pins and common extended electrodes 71 adjacent to each row of pin electrodes. The single row of electrodes requires that an extended symbol be formed by repeated selective discharges from the vicinity of selected pins 7d as the record medium moves beneath the head 12a to successive positions. The multiplicity of rows of electrodes in head 12b permits the formation of an entire symbol at once by simultaneous discharges from the vicinity of selected electrodes 'itl; this advantage is secured at the cost of additional selection and dischargeproducing equipment. The common electrodes '71 serve to form with their associated electrode pins (or pin electrodes) 'iil, gaps across which a disruptive electric discharge may be caused to occur and to serve as sources of charged particles which are deposited non-disruptively upon the charge-retentive surface of record medium Jltl.

This operation of the common electrode 71 is explained in much greater detail in application for United States patent Serial No. 734,253, Electrographic Recording Apparatus, tiled May 9, 1958 by Benn, Howell, and Sakurai and assigned to the assignee of the present application, now U.S. Patent No. 3,068,479, issued December 11, 1962. It is apparent that design considerations will determine Whether a single row of electrodes or a matrix of numerous rows is preferable for use in a particular embodiment of my invention, and that the choice in no wise affects the use of the present invention.

FIGURE 3 represents a portion of the dielectric of record medium It) after it has left the printing head 12. The dotted lines represent a pattern of electric charges which are in fact invisible. Passage through the developing station alters the appearance of the tape record medium I'll to that represented in FIGURE 4, where the charge patterns represented in FIGURE 3 appear as visible patterns delineated by adherent ink particles which are retained in place by the field of the electrical charges represented in FIGURE 3. It should be emphasized that the exact location and mechanism of storage of the electric charges in the dielectric of medium It? are not known at this time. It is known that passing the charged dielectric surface of tape Iii over a grounded metal roller does not discharge the image, since such treatment is standard in operative electric printers which are so designed that the latent charge pattern or image on the dielectric medium is developed after being passed over a grounded electrically conductive roller. It is not known whether the charges are located on the surface of the dielectric of a medium such as ill and are not discharged by the metal roller because there is in fact, only negligible actual contact between the dielectric and the rollers; or whether the charges are actually stored slightly below the surface of the dielectric and can flow only with difficulty and over an appreciable time to the surface, to be discharged. At all events, it is an experimental fact that simple forcible removal of the ink pigment from a developed dielectric record medium such as Ill does not remove or dissipate the electric charge pattern which originally attracted the, ink. Thus mere removal of the nk particle image does not place the record medium 10 in condition for the deposition of a new charge pattern, since the original charge pattern still persists.

After the developed medium It? has been observed sufiiciently at viewing station 26 in its passage from developing station 24, it moves to erasing station 25. At erasing station 25 a container I7 holds a mass of ink 18, into which the developed medium Ill is plunged. It passes over rollers 5 and between two sets of wipers 21 which may be of felt, which retain any ink particles which may be adhering to the medium. If the depth of the ink mass 18 is sufficiently great that its pressure near the bottom of container 17 prevents easy flow of ink particles through the mass, and thus shears the adherent ink particles away from the moving tape 14), the wipers may be dispensed with. At any event, it is necessary that ink once brought into intimate contact with the surface of medium It) be forcibly removed, and that more ink 18 be brought into contact with the dielectric surface of medium iii and then forcibly removed. This process permits the tape medium 10 to be removed from the mass of ink 18 at the end of its passage through erasing station 25 with no ink particles adherent to it, and devoid of its original charge patter It has been found that passage through four inches per second is sufficient to eliminate both ink and charge pattern. It is believed that this process works because the passage of the medium through the ink brings ink particles in contact with substantially every point of the surface of the medium 16), and that the stored charges in the medium are carried away by the ink particles which successively contact the surface.

The arrangement of the path of the medium 16 in FIGURE 1 is such that, after leaving the erasing station 25, the medium passes to drum 14, for further use.

An alternative arrangement of developing and erasing stations is represented in FIGURE 2. In FIGURE 2, the drive drum 14, ground electrode 13, electrostatic recording head 12, and apparatus 11 all perform exactly the same functions as in FIGURE 1. The record medium passes, after imposition of a charge pattern upon its dielectric surface, through a mass of ink 18 at developing station 22, where baffles 19 and vibrator 20 perform exactly the same functions as at developing station 24 of FIGURE 1. However, erasing station 23 is embodied in the same receptacle or housing as is developing station 22. The medium 10, after development, is carried up out of the developing station, passes horizontally through viewing station 26 for viewing, and then moves downward again to erasing station 23 where it plunges into the mass of ink 18, moves horizontally between two wipers 21, which may be of felt, and then turns upward again to move in a path which ultimately returns it to drum M for reuse.

An advantage of the embodiment of FIGURE 2 is that the ink removed from the medium 16 at erasing station 23 will ultimately flow back to replenish the supply at developing station 22, and thus the removed ink may be reused with no special provision to achieve this.

An extrcmly simple example of a combination developing and erasing station is to be found in FIGURES 6 and 7, FIGURE 7 being a profile View of the elevation of FIGURE 6, each being a section of the other. Actually, the effect of the sections is substantially as if a phantom drawing had been made in which the nearer wall of container 34 was removed to permit free vision of the working parts represented. In these figures, drum 69 is represented as supported on a shaft 70 which is supported by bearings and driven by rotation means not here represented. Record medium 10 is passed three times around drum 69, and, during the clockwise (as represented in FIGURE 6) rotation of drum 69, the tape is carried for two turns past a wiper 21, passing through the mass of electrically conductive ink 18 in the process of being erased. After its second trip past the wiper 21, the tape medium 1t passes under the recording head 12, where a new message is applied to it in the form of a pattern of invisible electric charges, which pattern is rendered visible by the adherence of ink 13 which occurs during the third trip of the medium 14 through the mass of ink 18, but without contact with the wiper 21. The developed and thus visible pattern is carried upward by movement of the medium 19, turns to move horizontally through viewing station 26, and then moves downward again to the drum 69 for repetition of the erase-recorddevelop view cycle.

FIGURE 8 represents, partly in section a generalized embodiment of my invention in a form not dependent for its operation upon the invention of Howell. In this figure, a cylinder 46, preferably electrically conductive, is mounted on a shaft 44 supported by bearings not shown so that it may. rotate in a clockwise direction and expose diiferent portions of its surface coating 41 of chargeretentive material successively to print head 42, to the developer contained in developing station 59, to the viewing station 45, and to the charge-neutralizing discharge electrodes 46, and the ink remover 4'7. In operations, a charge pattern is applied to coating 41 by the action of potentials provided from information and recording pulse source and control units 53 by conductors 52 to the electrodes of recording head 42. After a record has been made in one position of head 42, signals via channel 58 to motor 51 cause motor 51 to rotate and through shaft 50 drive gear 49 and pinion 48 so that worm 61 moves head 42 on guide 43 to a new position, where another record consisting of a charge pattern is deposited on coating 41. Since the time required to make such a record on coating 41 is very small compared with any readily obtainable speed of translation of head 42, it is equally feasible to drive head 4-2 at a constant speed, and apply recording potentials selectively to the pins of recording head 42 each time the head 42 has reached a position appropriate to the making of a new record. After the completion of a line of recording, motor 56, in response to signals received via channel 57 from information and recording pulse source and control unit 53, rotates the drum so that the recorded charge pattern is moved downward through a mass of developing medium 18, contained at developing station 59. The visible developing medium, which contrasts visually with the surface of coating 41, adheres to those parts of the surface of coating 41 where electric charges have been deposited by the action of head 42 already described. When the drum advances still further, a visible reproduction of the message will be aligned with viewing window 45. After the message has been observed at window 45, the drum 40 may be caused to rotate still further to present the charge pattern with its adherent developing medium to the action of brush 47 (which may alternatively be a vacuum device to remove developing medium) and to the brush discharge from electrodes 46 resulting from a high potential applied to them via conductor 54 from discharging potential source 55. The brush discharge will destroy or dissipate the charge pattern on the chargeretentive coating 41, and the brush 4'7 will remove the developing medium which was adhering to the charge pattern. It is obviously possible to employ this device for the continuous presentation of successive lines of recording to the window, with the same record medium, the coating 41 being used over and over again. 'It will be observed that in this embodiment of my invention, charge erasure and removal of developing medium, or ink, does not occur in the same container where the development of the charge pattern occurs, nor need the used developing medium necessarily return to the developing station although it is quite feasible to arrange for it to fall back into the container of the developing station for reuse.

The dotted ground to the shaft 44 of cylinder 40 is intended to indicate grounding through the bearings and the machine frame, although provision of a special slipring and brush for grounding is possible, it necessary. It is 'most desirable that the cylinder 40 be electrically conductive and be grounded, in order that the field across the coating 41 be definitely oriented both under printing or recording head 42, and opposite electrodes 46.

Clearly, the particular mechanical arrangements of FIGURE 8 are susceptible of infinited variation. Cylinder 40 might be replaced by a disk. Head 42 might be widened and the corresponding circuitry in unit 53 might be arranged so that an entire line on coating 41 might be recorded at once, in which case there would be no need for worm 61 and elements 48, 49, 5t) and 51. However, the sp ed of human reading and comprehension is far less than such a stratagem could saturate, and so the present embodiment of FlGURE 8 is believed potentially more economical for the particular requirements of a visual display unit.

FIGURE 9 represents another embodiment of my invention which provides means for returning removed ink 1 3 to the developing station 241 for use, but without employing the erasure method of Howell. Medium 10 is advanced by rotation of drive roll 14 and passes between ground electrode 13 and opposed printing head 12, whose electrodes are appropriately excited by printing pulse source 11 and deposited upon the charge-retentive surface of medium 11) change patterns representative of the symbols to be displayed. The medium It) then advances over an idler 9, (and moves upward into developing station 2 similar to developing station .24 except that a part of its upper portion is not covered, for a reason to be disclosed hereinafter, Passage through the mass of ink 18 at developing station 24} leaves medium It) with a developed and visible pattern upon its surface. Further advance of medium .10 causes the visible pattern to be presented for viewing at viewing station 26, which is represented in FIGURE 9, so oriented that the message presented thereat is not shown in the figure. After viewing, the pattern moves by advance of the medium 10 over another idler 9, and downward past electrodes 461, which, from the high potential applied to them by discharging potential source 55, produce a brush discharge in the ambient air, which discharge has the effect of discharging the charges on the medium 16 and on the particles of ink 18 adherent to it. Ground electrode 64 is opposed to electrodes 461, in order .to assure a concentration of field near them without exclusive reliance upon the continuity of the conductive backing of medium It} which electrode 6@ may contact. Further progress of medium 10 carries the medium 10, and any ink particles which remain adherent even in the absence of charge, to brush 471, which differs in shape from brush 47 in that it is given a tapered side so that it will steer the advancing particles of ink 18 to one side of the medium .10, in order that they may fall by gravity through the uncovered portion of the top of developing station 241, this uncovered portion being the difference between station 241 and station 24 of FIGURE 1. The medium 10, divested of its charges and its attached particles of ink .18 then moves over another idler 9, and proceeds downward to drive roller id, to begin another cycle of use. It .is evident that the embodiment of FIGURE 9, while not utilizing the erasure method of Howell, basically [meets the requirements for a data display device which can use and repeatedly reuse record medium 10 and ink d8 for display of data or other symbols.

The adherence of ink 13 to medium 10 is sufificiently firm that it is feasible, for example in the embodiments of FIGURES 1, 2, 6, 7 and 9, to run the tape-form medium over idlers at such an angle that the medium may be displayed as a horizontal line of tape in a vertical plane, like a line of tape fastened to a vertical :board, and the viewing station 26 or similar station will then be located vertically, ninety degrees from the positions shown. This may be preferable in some uses. The embodiments shown Were chosen as being clearer and more readily understood from drawings and thus better adapted to the teaching of the invention. The art of running continuous belts or tapes over i-dlers .at various angles is so extremely well known from, inter alia, the use of belts for power transmission during the last century, that further discussion has been deemed unnecessary.

The invention of Howell has been found to function to erase charge patterns upon dielectric media having an electrically conductive backing, and also to erase specific charge patterns upon dielectric media not having such a backing; but for the latter media, repeated erasures in a short period of time may build up a background charge which tends to produce a somewhat dark visible background upon development. However, dielectric media not provided with a conductive backing have been found less satisfactory, in general, than media provided therewith, and the inferiority of the former kind of media with respect to erasure is no greater than their inferiority in other aspects of electrostatic recording. Thus those forms of my own invention which apply Howells invention are applicable wherever and in the same degree as the invention of Howell is applicable to a given recording medium. It is of course apparent that the basic principle of providing a common container for the ink employed in develop- [ing and the ink employed in erasing both the visible and the electrical pattern may lead to an endless variety of embodiments; thus the developing station and the erasing ca station may each be provided with separate housings which are made into a common container by a duct connecting them and suitable to permit the excess of ink removed in the erasing station to flow into the developing station. Alternatively this principle of my invention may be practiced by locating the erasing station higher than the developing station, and having a discharge from the ink removed in the erasing station to fall into the ink container of the developing station, so that the space between the two containers, through which the ink may fall from one container to the other, renders them effectively common even though the space between them is not specifically walled off or delimited.

It should be observed that, because of the extremely small currents involved in the development process, and the high potentials available, the criteria of conductivity of the ink are quite different from those usually applied in even what is known as Wealccurrent engineering. Thus, glass beads alone may be employed for development of latent electrostatic images. They are not mixed with other material to form a tribo-electric combination, and show no observable tendency to acquire charges in handling; it appears that the film of moisture which they acquire in normal ambient atmosphere, or other surface materials, provide conductivity sufficient for them to function.

Having described my invention and its use, I claim:

1. A message display device comprising: a dielectric film medium forming a continuous loop, means for supporting said dielectric medium and for moving it in a circuit past an electrical recording station, a developing station, a viewing station, and an erasing station, wherein said electrical recording station comprises a multiplicity of discharge electrodes and an anvil electrode, means for presenting said discharge electrodes in proximity to one face of said dielectric film medium and said anvil electrode in abuting relationship to the opposite face of said medium in said recording station and, under the influence of recording potentials applied to said electrodes, depositing electric charge patterns on said medium, said developing station comprises a reservoir adapted to contain a quantity of conductive developing ink and adapted to permit the passage through said reservoir of the charged surface of said dielectric medium in intimate contact with and immersed in said developing ink whereby said conductive ink is caused to adhere to said electric charge patterns and thereby render them visible, said viewing station comprises means superimposed adjacent to a portion of the path of the said dielectric film medium adapted to enable direct viewing by an observer, and said erasing station comprises means for removing from said dielectric medium the static electrical charges and the said adherent conductive developing ink; a signal source; means for receiving signals from said signal source and for applying recording potentials in accordance with the received signals to the said discharge electrodes of the said electrical recording station; and control means for controlling the means for moving the said dielectric film medium.

2. A message display device as claimed in claim 1, characterized by the fact that the dielectric film medium is a sleeve over electrically conductive cylinder which constitutes at least partly the means for supporting the said dielectric medium.

3. A message display device comprising: a continuous loop of dielectric film, means for moving said loop of film along its periphery, means for establishing on said dielectric film a pattern of invisible electrically charged areas representative of symbol information, means to apply symbol information signals to said establishing means, said establishing means comprising an electrostatic recording head, an electrode opposed to said head, said film being moved between said head and said electrode, said head being responsive to said applied signals to establish said charged areas in a shape corresponding to the symbol information applied, conductive ink reservoir means responsive to immersion of said dielectric film and containing conductive ink in quantity for rendering said electrically charged areas distinguishably visible, viewing station means for exposing directly to an observers view the said electrically charged areas thus rendered visible, and means for restoring without damage to said dielectric film the said electrically charged areas thus rendered distinguishably visible to an uncharged and undistinguishable condition and available for establishing new electrically charged areas upon said dielectric film.

4. A message display device comprising: a continuous loop of dielectric film of high resistivity, means for moving said loop of film in a closed path, means for establishing on said dielectric film a pattern of invisible electrically charged areas representative of symbol information, means including a store of visibly distinguishable particulate ink for rendering said electrically charged areas distinguishably visible by the adherence to said charged areas of said ink, means for exposing directly to an observers view the said electrically charged areas thus rendered distinguishably visible, and means for restoring to an uncharged condition the said electrically charged areas thus exposed to an observers view and for removing from the said dielectric film and returning to the said store for repeated use the said particulate ink.

5. A message display device comprising: at an initial location, a portion of record medium having a dielectric charge-retentive surface, first means comprising a plurality of pins responsive to symbol information signals to selectively discharge in accordance with the symbols for establishing on said charge-retentive surface a pattern of invisible electrically charged areas representative of said symbols, second conductive particulate ink reservoir means adapted for immersion of said record medium in said conductive particulate ink for rendering said electrically charged areas distinguishably visible by the adherence to said charged areas of distinguishable particulate ink, third means for exposing to an observers view the said electrically charged areas thus rendered distinguishably visible, and fourth means for restoring to an uncharged condition the said electrically charged areas and for removing from the said charge-retentive surface the said distinguishable particulate ink without damage to said dielectric charge-retentive surface; and means for advancing the said record medium successively past said first, second, third and fourth means and for finally advancing the said record medium from the said fourth means back to the said initial location.

6. A data display device adapted to be connected to a data and control signal source and to receive and display data from said source in accordance with control signals therefrom, comprising, in combination: a rotatable metal drum supported on a shaft; controllable means for rotating the said drum, adapted to be connected to and controlled by signals from the said data and control signal source; a flexible, metal-backed continuous dielectric charge-retentive belt of high electrical resistivity wrapped in several turns around the said drum with the said metal backing in contact with the said drum; a chamber partially enclosing the said drum; a recording or printing station adjacent to the said drum for applying to the exposed dielectric face of the said belt electric charges in patterns representative of information in accordance with electric impulses received from the said data and control signal source, to which the said recording station is adapted to be connected; a developing station adjactnt to the said drum and located in the said chamber for exposing particles of distinctively colored particulate developer to the attractive force fields of the said charge patterns, whereby the said charge patterns are rendered visible by the adherence to them of the said particulate developer; a viewing station external to the said chamber for exposing to the view of an observer a portion of the said belt bearing the said charge patterns rendered visible by the said particulate developer; an erasing station in the said chamber for removing the said charge pattern and the said adherent developer; and freely rotatable undriven belt carrier means, or idlers, disposed to support the said belt for free motion from the said drum to enter into the said viewing station and to exit from the said viewing station and return to the said drum in potentially continuous motion repeatedly over the path here recited.

7. A data display device comprising a record medium, first means for establishing on the said record medium force fields representative of an image to be displayed; second means for rendering said image visible by causing a contrast particulate ink to adhere to the surface of said record medium by the action of said force fields; third means for displaying said visible image; fourth means for removing said adherent particulate ink from and destroying the said force fields upon the said record medium; said means further comprising means whereby the said adherent particulate ink after removal from the said medium by the said fourth means is returned to said second means for reuse.

8. A device for displaying visible symbols comprising a record medium adapted to have established on it localized invisible electrical charges over areas representative of such symbols, first means for so establishing such force fields, second means for exposing a visible developer to be attracted by such force fields to the surface of the said record medium and thus delineate visibly the areas where such force fields exist, and third means for simultaneously removing such developer from the surface of the said record medium and destroying the said force fields existing at the surface of the said record medium: said third means being positioned relative to the said second means such that the developer removed by the said third means is moved by gravity to the said second means and there is available for reuse as a developer.

9. A data symbol display device comprising an opaque charge-retentive medium comprising a dielectric surface and a conductive backing, means to produce electric charges on the said medium, said charges forming symbols; a reservoir of conductive particulate ink, means to draw said medium in a path through said ink, said path through said ink being of amount such that said charges are developed to render them visible, viewing station means located adjacent said medium so as conveniently to display the said visible symbols to view by an observer; and means comprising additional conductive particulate ink and means to provide a path therethrough sufficient to remove from the said charge-retentive medium after said display both the said electric charges and the said visible particulate developer and render the said chargeretentive medium available for repeated use.

iii. A data display device comprising a medium of high electrical resistivity having an electrically conductive opaque backing, means to produce electric charges on the said medium, said charges forming symbols; means to apply conductive but uncharged particulate developer to said charges to make the charges visible; means to display the said symbols to the direct view of an observer; and means to remove from the said medium after said display the said electric charges and the said developer, said last-named means comprising at least one electrode, a high potential source to produce a brush discharge in ambient air and a ground electrode opposed to said at least one electrode to thereby discharge said charges and developer and a brush to brush oif developer which remains adherent in the absence of charge.

13.. In a device for displaying visible symbols representative of intelligence comprising a record medium adapted to have established on it localized invisible force fields over areas representative of such symbols, first means for so establishing such force fields, second means, including a reservoir for containing a visible developer,

for exposing said visible developer to be attracted by such force fields to the surface of the said record medium and thus delineate visibly the areas where such force fields exist, third means for viewing directly the visibly delineated areas of the surface of said recording medium after attraction of said developer thereto, and fourth means for simultaneously removing such developer from the surface of the said record medium into a receptacle therefor and destroying the said force fields existing at the surface of the said record medium; the said reservoir for the said second means and the said receptacle for the said fourth means comprising a common container.

12. A data display device comprising a continuous loop of dielectric material, a drum, a reservoir of developer material, said drum being partially embedded along its length in said developer material, said loop being Wound spirally a plurality of times around said drum, an electrical recording station comprising a recording head to apply a pattern of electrically charged areas to said loop, said recording station being positioned outside of said developer material in aligned facing relationship to said loop and the plane of the drum surface around which said loop is wound, a viewing station, wiper means positioned in closely adjacent relationship to said drum and embedded in said developer material adjacent at least one of said loop drum windings, means to advance said dielectric material loop around the periphery of said drum past said recording station to enable applyiing of charged area pattern information, through said developer material an amount such that said charged areas are developed, thence from said developer material past said viewing station to enable viewing of said charged and developed areas, thence back into said developer material and between said drum and said Wiper means so as to effect erasing of both said developer material and said charged areas from said charged and developed dielectric material, and thence past said recording station in endless loop recycling arrangement.

13. The apparatus of claim 12. wherein said drum is rotatably mounted, means to rotate said drum, said drum having cylindrical surface sections so that said drum surface section forms the anvil electrode in recording in said aligned loop, head and drum facing relationship wherein said recordin station comprises said recording head and said drum surface section, said drum having a second drum surface section forming together with said wiper and said developer material the means whereby said visi ble developer and said charges on said loop surface are removed, said dielectric material loop being rotatably spirally looped at least two times around said drum so as to be carried successively at least one turn past said Wiper and passing through the mass of developer in the process of being erased, thence being looped so as to pass on the next turn under said recording head to receive a message pattern of electrical charges, thence passing through the developer material to render said charge pattern visible, said viewing station being positioned outside of said developer, said medium being further looped to pass said viewing station and said medium being still further looped to move adjacent to said drum past said wiper for recycling of the erase-recorddevelop-view cycle.

14. A data display device comprising a medium of high electrical resistivity having an electrically conductive opaque backing, means to produce electric charges on the said medium, said charges forming symbols; means to apply conductive but uncharged particulate developer to said charges to make the charges visible; means to display the said symbols to the direct view of an observer; and means to remove from the said medium after said display the said electric charges and the said developer, said lastnamed means comprising at least one electrode, a high potential source to produce a brush discharge in ambient air and a ground electrode opposed to said at least one electrode to thereby discharge said charges and developer and a brush to brush off developer which remains adherent in the absence of charge, said data display device further comprising a right circular cylinder having an electrically conductive surface providing said ground electrode and said electrically conductive medium backing, said cylinder being covered with an electrially insuiating charge-retentive coating to provide said medium with its hi h electrical resistivity; support means to rotatively support the said cylinder; drive means to cause the rotation of said cylinder; grounding means to cause the electrical potential of said cylinder to remain substantially constant with respect to a reference point; said means to produce electrical charges on the said medium comprising recording means adjacent to the periphery of said cylinder to apply to the portion of said coating lying between the said cylinder and the said recording means, said electric charges in patterns to be rendered visible; said means to apply conductive but uncharged particulate developer to said charges to make the charges visible comprising developing means adjacent to the periphery of said cylinder to expose to attraction by the fields of said electric charges visible developing medium adapted to delineate the said patterns of the said charges; said means to display the said symbols to the direct view of an observer comprising display means adjacent to the periphery of the said cylinder to expose said patterns thus delineated to inspection by an observer; said means to remove from the said medium after said display the said electric charges and the said developer comprising erasing means adjacent to the periphery of said cylinder to remove the said developing medium adherent to the said electric charges and to nullify the said electric charges.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES instruments, vol. 25, Issue 4, page 488, April 1952.

IRVING L. SRAGOW, Primary Examiner.

NEWTON N. LOVEWELL, EDWARD V. BENZ-1AM,

Examiners. 

1. A MESSAGE DISPLAY DEVICE COMPRISING: A DIELECTRIC FILM MEDIUM FORMING A CONTINUOUS LOOP, MEAN FOR SUPPORTING SAID DIELECTRIC MEDIUM AND FOR MOVING IT IN A CIRCUIT PAST AND ELECTRICAL RECORDING STATION, A DEVELOPING STATION, A VIEWING STATION, AND AN ERASING STATION, WHEREIN SAID ELECTRICAL RECORDING STATION COMPRISES A MULTIPLICITY OF DISCHARGE ELECTRODES AND AN ANVIL ELECTRODE, MEANS FOR PRESENTING SAID DISCHARGE ELECTRODES, IN PROXIMITY TO ONE FACE OF SAID DIELECTRIC FILM MEDIUM AND SAID ANVIL ELECTRODE IN ABUTING RELATIONSHIP TO THE OPPOSITE FACE OF SAID MEDIUM IN SAID RECORDING STATION AND, UNDER THE INFLUENCE OF RECORDING POTENTIALS APPLIED TO SAID ELECTRODES, DEPOSITING ELECTRIC CHARGE PATTERNS ON SAID MEDIUM, SAID DEVELOPING STATION COMPRISES A RESERVOIR ADAPTED TO CONTAIN A QUANTITY OF CONDUCTIVE DEVELOPING INK AND ADAPTED TO PERMIT THE PASSAGE THROUGH SAID RESERVOIR OF THE CHARGED SURFACE OF SAID DIELECTRIC MEDIUM IN INTIMATE CONTACT WITH AND IMMERSED IN SAID DEVELOPING INK WHEREBY SAID CONDUCTIVE INK IS CAUSED TO ADHERE TO SAID ELECTRIC CHARGE PATTERNS AND THEREBY RENDER THEM VISIBLE, SAID VIEWING STATION COMPRISES MEANS SUPERIMPOSED ADJACENT TO A PORTION OF THE PATH OF THE SAID DIELECTRIC FILM MEDIUM ADAPTED TO ENABLE DIRECT VIEWING BY AN OBSERVER, AND SAID ERASING STATION COMPRISES MEANS FOR REMOVING FROM SAID DIELECTRIC MEDIUM THE STATIC ELECTRICAL CHARGES AND THE SAID ADHERENT CONDUCTIVE DEVELOPING INK; A SIGNAL SOURCE; MEANS FOR RECEIVING SIGNALS FROM SAID SIGNAL SOURCE AND FOR APPLYING RECORDING POTENTIALS IN ACCORDANCE WITH THE RECEIVED SIGNALS TO THE SAID DISCHARGE ELECTRODES OF THE SAID ELECTRICAL RECORDING STATION; AND CONTROL MEANS FOR CONTROLLING THE MEANS FOR MOVING THE SAID DIELECTRIC FILM MEDIUM. 